This invention relates to phenolic resole resins which contain small quantities of aliphatic hydrocarbylphenol having from 9 to 17 carbon atoms in the hydrocarbyl group, their manufacture and use for making wood-product laminated composites and such composites manufactured from the resins. The resins will generally contain urea in a quantity sufficient to lower the viscosity of the resin and to scavenge formaldehyde. By the term "hydrocarbyl" we mean a monovalent group containing only the elements of hydrogen and carbon.
It has been found that from about 0.2 to about 5% of an aliphatic hydrocarbylphenol having from 9 to 17 carbon atoms in the hydrocarbyl group when polymerized with formaldehyde and phenol in an aqueous alkaline medium to form a phenolic resole resin or when post-added to an alkaline phenol-formaldehyde aqueous resin solution provides adhesives for the manufacture of wood-product laminated composites wherein the resulting composites have improved internal bond strengths, durability, decreased water absorption and thickness swell properties in comparison with phenolic resole resins which do not contain the specified hydrocarbylphenols in the indicated quantities of this invention.
Phenol-formaldehyde resole resins represent a large portion of the adhesive binders used in the manufacture of wood-product laminated composites. Phenol-formaldehyde resole resins are frequently used as laminate binders in the manufacture of wood-product laminated composites such as veneer products, e.g., plywood and LVL (laminated veneer lumber), as well as wood-particle composites, e.g., particleboard, waferboard, and OSB (oriented strand-board). In most cases, the laminated composites are in the form of panels.
Liquid phenolic resole resins bind as thermosets which are typically cured via hot pressing. Hot pressing is done under pressure with heat supplied via platens heated by hot oil, electricity, or steam. Phenolic thermoset curing methods include RF-curing (radio frequency) and steam injection pressing.
Traditionally, liquid phenol-formaldehyde resole resins constituted the predominant type of adhesive used as wood-product binders for products such as OSB and plywood. Recently, isocyanates such as PMDI (poly(methylenediphenyl-4,4'-diisocyanate)) have come into use as wood-product laminate composite adhesives for manufactured products. Isocyanates offer faster cure speeds, reduced tendency for water absorption, and lower overall manufacturing costs in comparison with phenolic resole resins. Also, less of the isocyanate is required.
A draw-back of wood product laminated composites bound with isocyanates is that they are prone to degradation because of lower rigidity and moisture induced internal panel stresses as well as health risks in the mill. This is particularly the case with non-veneer laminated composites. Isocyanates are especially prone to this form of degradation since they lack the durability of three-dimensional network crosslinking density inherent with phenol-formaldehyde resins. In order to further improve liquid phenolic resins and make them more competitive against isocyanates we began researching ways to improve such resins. We have found that the incorporation of certain small amounts of hydrocarbylphenol having from 9 to 17 carbon atoms in the hydrocarbyl group when polymerized with aldehyde and phenol in the manufacture of the resin polymer or when added to a preformed phenol-aldehyde resin which is eventually coated on wood products and bound under heat and pressure to form composite panels impart improved properties to the wood-product laminated composites.
The prior art shows the use of aldehydes reacted with various phenolics such as phenol, naphthol, and various hydrocarbylphenols and mixtures thereof for use in the manufacture of resole resins as well as the use of certain of the resole resins for the manufacture of composite panels and other materials. The prior art also shows the use of urea dissolved in certain resole resins for the manufacture of composite panels. However, the prior art does not show or suggest that the small quantities of the aliphatic hydrocarbylphenols used in this invention when polymerized with phenol and an aldehyde as part of the manufacture of a phenol-formaldehyde-hydrocarbylphenol resole resin or when such hydrocarbylphenols are simply dissolved in a preformed phenol-aldehyde resole resin provide superior and unexpected properties in the manufacture of composite panels, with or without urea.